Stephen Hawking (1942-2018)

Roger Penrose writes in the Guardian, providing a scientifically precise summary of Hawking’s accomplishments as a physicist (worth reading in full at the link). Penrose and Hawking collaborated to produce important singularity theorems in general relativity in the late 1960s. Here is a nice BBC feature: A Brief History of Stephen Hawking. The photo above …

More

Gork revisited, 2018

It’s been almost 10 years since I made the post Are you Gork? Over the last decade, both scientists and non-scientists have become more confident that we will someday create: A. AGI (= sentient AI, named “Gork” :-)  See Rise of the Machines: Survey of AI Researchers. B. Quantum Computers. See Quantum Computing at a Tipping …

More

Big Ed

Today I came across a recent interview with Ed Witten in Quanta Magazine. The article has some nice photos like the one above. I was struck by the following quote from Witten (“It from Qubit!”): When I was a beginning grad student, they had a series of lectures by faculty members to the new students about …

More

Steven Weinberg: What’s the matter with quantum mechanics?

In this public lecture Weinberg explains the problems with the two predominant interpretations of quantum mechanics, which he refers to as Instrumentalist (e.g., Copenhagen) and Realist (e.g., Many Worlds). The term “interpretation” may be misleading because what is ultimately at stake is the nature of physical reality. Both interpretations have serious problems, but the problem …

More

Are quanta particles or waves?

Are quanta particles or waves? The title of this post is an age-old question isn’t it? Particle or wave? Wave or particle? Many have rightly argued that the so-called “wave-particle duality” is at the very heart of quantum weirdness, and hence, of all of quantum mechanics. Einstein said it. Bohr said it. Feynman said it. …

More

Gell-Mann on quantum foundations

Google knows enough about me that my YouTube feed now routinely suggests content of real interest. A creepy but positive development ;-) Today YouTube suggested this video of Murray Gell-Mann talking about Everett, decoherence, and quantum mechanics. I had seen this video on another web site years ago and blogged about it (post reproduced below), …

More

EPR and Bell for pedestrians

My old friend Mark Alford (WUSTL) was on campus last week for the inaugural meeting of the FRIB-TA (Facility for Rare Ion Beams Theory Alliance). Over beers he told me he had come up with a pedagogical way to explain Bell’s inequality in a single picture. Here it is. Ghostly action at a distance: a …

More

Schwinger meets Rabi

Seventeen year old Julian Schwinger meets Columbia professor I. I. Rabi (Nobel Prize 1944) and explains the EPR paper to him. Climbing the Mountain: The Scientific Biography of Julian Schwinger [p.22-23] … Rabi appeared; he invited Motz into his office to discuss ‘a certain paper by Einstein in the Physical Review’! Motz introduced Julian and …

More

Instability of Quantum de Sitter Spacetime

New paper! We show that quantum effects (in particular, the horizon temperature originally discovered by Gibbons and Hawking) modify the geometry of de Sitter spacetime. Instability of Quantum de Sitter Spacetime (http://arxiv.org/abs/1501.00708) Chiu Man Ho, Stephen D. H. Hsu Quantized fields (e.g., the graviton itself) in de Sitter (dS) spacetime lead to particle production: specifically, …

More

Quantum GDP

  “It’s been only half jokingly said that today a third of GDP is attributable to quantum mechanics,” — former Lockheed CEO Norm Augustine. I’ve heard the one third or 30% of GDP figure from time to time, but have never seen a detailed analysis. A list of modern technologies that arose from quantum mechanics …

More

Patterns on the sky

I’m busy reviewing ~200 promotion and tenure cases for my day job, so I don’t have much time to post about the BICEP2 observation of primordial gravitational waves via their effect on the polarization of the cosmic microwave background (CMB). Instead, I refer you to Sean Carroll, Lubos Motl and Liam McAllister (guest poster at …

More